Turbo to non turbo

[GOKIWI]

While it is very possible it is very expensive , time consuming and you will also need to be a good fabricator or at least have access to one.

If you turbo a standard nasp engine you will not be able to go for more than a few psi boost as the internals will not take much more and that cost wont justify the gain.

Things you will need.

New camshaft's or least cam's ground to suit turbo type use
New pistons , lower compression
Stronger oil pump, you now have to pump oil to the turbo bearings
Secondary water pump, you will need water circulating the turbo to keep it cool after use
Inlet manifold and plenum chamber
Exhaust manifold
Exhaust system
Turbo
Intercooler
Oil cooler
Oil and Water lines
ECU 
Pipework, including oul feed and return to the turbo
Electrical harness
Brackets and misc fastners
Potentially stronger engine and gearbox mounts
Stronger clutch and flywheel
Maybe even better brakes 

My Leon for example is rated (flywheel figures) at 225BHP but to get to 300BHP cost over £2000 so that works out at £26 per 1HP gained.